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Case Study: Wind Tuning in the Adriatic using Scatterometry

The city of Venice is one of the places in Europe most vulnerable to storm surges, being flooded several times a year. The venetian 'acqua alta' is typically a combination of high tide, seiche and a storm surge. A barrier system, MOSE, is being built to protect the city, however for the barrier to be most effective accurate predictions of high water are essential.

The ESA eSurge-Venice project has been set up to help improve the modelling of storm surges in this region by the use of satellite data.

One area that the project has been looking at is improving the wind forecast used in the model. Winds in the Adriatic Sea tend to be underestimated by atmospheric models, due to the complicated local terrain around the shore. High resolution scatterometry, such as that provided to eSurge by KNMI/OSI-SAF, has the potential to improve this.

The wind speed from ECMWF is tuned using scatterometer data, and then averaged over a given temporal range around a surge event. (A similar process is followed for wind direction.) The statistics show that the tuned data has a much longer tail, meaning that extreme events have higher wind speeds than predicted from ECMWF winds alone.

The original and corrected wind fields were then used as inputs to the SHYFEM model. The corrected fields are a closer match to observations, and in particular give a much better match to the skew surge.

The conclusion is that assimilating scatterometer data does give a significant improvement in surge forecasting. This shows the importance of accurate winds in surge models. Perhaps surprisingly though, there is only a low dependence on spatial resolution, with temporal resolution being more important.